FACT SHEET

FLOOD CONTROL STRUCTURES ADDRESSING IMPACTS ON INFRASTRUCTURE: PREPARING FOR CHANGE

Flood control structure in Iloilo, Philippines. Photo Credit: IRG

Changes in climate will threaten the efficacy, adequacy, and durability of flood control structures and their continued services. FLOOD CONTROL STRUCTURES INCLUDE: • Dikes Since flood control structures provide defense against frequent, • Spurs small in and , rising sea levels, and storm surges, • climate change impacts on these structures may significantly affect the • communities relying on their protection. Such impacts have implications for urban stability, economic growth and trade, and food and water availability. FLOOD CONTROL STRUCTURES SUPPORT: • Urban programs These structures and their services can be protected with adaptation • Economic growth and trade strategies that include fortifying existing structures and updating design • Food and water availability standards to accommodate future climate changes.

FLOOD CONTROL STRUCTURES ARE development practitioners can help ensure the lasting effects of INTEGRAL TO DEVELOPMENT PRIORITIES development projects and programs in vulnerable areas. Flood control structures are designed to protect coastal and - CLIMATE STRESSORS CAN SIGNIFICANTLY areas, including urban and agricultural communities, homes, and other IMPACT FLOOD CONTROL STRUCTURES economically valuable areas, and the people located within them. These structures are used to divert flows of water, by re-directing rivers, slowing AND THEIR SERVICES natural changes in embankments and coastlines, or preventing inundation Like many other types of infrastructure, flood control structures are of vulnerable coastlines or . Dikes, spurs, levees, and seawalls often designed to last several decades. Several climate stressors affect often act as the first line of defense against overflowing rivers, floods, the efficacy and durability of flood control structures, including changes in storm surges, and—in the longer term—rising seas. By keeping water out, precipitation, sea levels, extreme events, and resulting storm surges. Flood flood control structures lessen harm to physical infrastructure and help to control structures are unique in that they can be compromised by the ensure continuation of communities’ economic and social activity. same stressors they are designed to withstand. For example, increases in the intensity and frequency of floods could overwhelm these structures, But flood control structures do not completely eliminate risk. Flooding causing them to fail. These stressors will grow in importance as climate may occur if the design water levels are exceeded. If poorly designed, change continues to alter their intensity, variability, and accompanying constructed, operated or maintained, these structures can increase risk hazard potential. by providing a false sense of security and encouraging settlements or economic activity in hazard-prone areas. Potential impacts will depend on a variety of factors that affect the vulnerability of these structures. For example, if sea walls are constructed Nevertheless, many development programs rely on these structures to in areas that are experiencing land subsidence, they will be more maintain program objectives, including continued food and water supplies, vulnerable to storm surges and . Climate change risks vary economic activity, and protection from storms and floods. For example, in relative importance, with a range of cost implications, compounding urban initiatives (e.g., urban transport projects) in coastal cities like Dhaka, effects, and impacts on development objectives. Failures of flood control Bangladesh necessarily rely on effective flood control structures, such structures can result in dire consequences for the services provided as pump stations and dikes, to maintain program effectiveness in the and investments made by the development community. Table 1 provides short-term. By supporting the climate-resilient design, construction, several examples of potential climate change impacts on flood control and maintenance of flood control structures, USAID and other structures.

ADDRESSING CLIMATE CHANGE IMPACTS ON INFRASTRUCTURE: PREPARING FOR CHANGE FLOOD CONTROL STRUCTURES 1 Table 1. Examples of Potential Climate Change Impacts on Flood Control Structures and Services

Flood Control Structures and Services Precipitation Change • Failure of existing flood control structures due to increased flooding from increased precipitation • Weakened embankments or inefficient impervious core due to and liquefaction from recurring, intense flooding

Sea Level Rise • Overflowing of older structures built to standards that do not integrate sea level rise • Weakening of flood control structures due to land subsidence and erosion combined with sea level rise • Inundation of structures in low-lying lands due to failure of flood control structures • Overpowering of structures due to increased height of waves, , and surges • Weakened or damaged structures (e.g., cracks in critical junctures) due to repeated storm surge

Extreme Events • Damage to and destruction of flood control structures due to sudden freeze-thaw cycles or the combined forces of cascading extremes such as cyclones, , heavy precipitation • Breaches of structure leading to temporary and permanent inundation

DEVELOPMENT PROGRAMS CAN INCLUDE addition to hydrologic, environmental, and ecosystem impacts. Adaptation actions should be integrated into the overall risk management strategy for FLOOD CONTROL STRUCTURE-RELATED flood control structures. ADAPTATION Adaptation priorities should be selected based on decision-makers’ To reduce climate change impacts on flood control structures and the assessment of the following four key factors (presented with illustrative resulting damage and destruction to coastal and low-lying communities, question; refer to Overview for further guidance): development practitioners must adapt flood control structures to future climate stressors. Adapting flood control structures will protect • Criticality – What is the hazard potential of failure of these investments in a variety of sectors, including transportation, energy, and structures, including population and value of assets in the area urban programs. protected by the structures?

The resilience of flood control structures can be increased in many ways. • Likelihood – Given climate projections, how likely is it that this For example, flood control structures should be built to higher levels structure will be weakened or overwhelmed by climate change? and with more resilient materials and designed to withstand repeated • Consequences – Will climate changes lead to breach, overtopping, or and more extreme floods. Similarly, in designing flood control structures, complete failure of these structures or destabilize the embankments? If USAID and other development organizations should consider, where the structure fails, what damage and destruction will ensue? feasible, constructing back-up structures to provide services in case of • Resources available – Can the structure be fortified at low cost? failure. In addition, design standards should incorporate sea level rise Do new structures need to be built to provide adequate protection projections, as well as the hydrology and physiography of the watershed to services? Are there certified specialized engineers to design, construct, minimize or avoid unintended adverse impacts. inspect, and maintain these structures in the target areas? It is critical that trained and registered engineers design, implement, and An integrated, climate-resilient approach to flood control management review new construction and improvements to ensure stability, since will ensure that development program outcomes are durable and untested flood control structures may constitute a direct threat to human long-lasting. Climate change projections should be deliberately and life. In addition, communities should avoid promoting an unfounded sense knowledgeably included in the various project cycle stages, including the of security as any structure may fail in extreme circumstances. design, construction, and maintenance of flood control structures. Different To understand the implications for flood control structures, decision options exist to mitigate the impacts of these climate stressors, including makers should identify plausible future climate scenarios to understand structural changes (e.g., changes to embankment slopes) and policy how relevant factors—such as sea levels and extreme event intensity— changes (e.g., changes to codes, relocation, designing redundancy are projected to change. Using this information, decision makers can plans). Table 2 provides illustrative examples of adaptation options for identify needed changes to the design, construction, and maintenance of flood control structures, and shows the overall approach to assessing and structures. Development practitioners must understand the vulnerabilities addressing climate risks using the Climate-Resilient Development (CRD) of different structures, based on location, design, and construction in Framework. See the Overview for further guidance.

2 FLOOD CONTROL STRUCTURES ADDRESSING CLIMATE CHANGE IMPACTS ON INFRASTRUCTURE: PREPARING FOR CHANGE Table 2. Examples of Flood Control-Related Actions by Project Cycle Stage

Project Cycle Stage Project Cycle Actions

• Identify flood control-related development goals important to the country, community, or sector you are working with • Identify inputs and enabling conditions necessary to achieving those goals • Consider the impacts of climate and non-climate stressors on those inputs • Assess climate impacts to understand how the design, construction, and maintenance of flood control structures may need to change • Evaluate climate-related risks amidst all existing risks to flood control structures and associated services • Evaluate social, hydrologic, environmental, and ecosystem impacts of the proposed action • Evaluate non-climatic factors, such as land use changes, to understand how they may ameliorate or exacerbate effects from floods Adaptation Options (Examples) ACCOMMODATE/MANAGE PROTECT/HARDEN RETREAT/RELOCATE • Develop redundant structures or services • Update design standards to integrate • Plan for community relocation that can be relied upon if structures fail projected sea level rise and storm • Explore natural resource management surge • Increase inspection frequency to ensure approaches to increase storage in the Planning structures are enduring climate change • Fortify embankments to counteract watershed or break waves, such as Policy Changes pressures effects of increased coastal erosion establishment of mangroves Project Development • Design flood risk-management plans with • Update zoning codes for coastal land to both ecosystem- and construction-based establish natural buffer zones adaptation options Adaptation Options (Examples) ACCOMMODATE/MANAGE PROTECT/HARDEN RETREAT/RELOCATE • Increase resources for more frequent • Use permeable materials in select • Relocate communities further inland or maintenance and repairs locations to allow for better away from flood basins Construction absorption of water Operation • Temporarily evacuate areas • Use improved asphalt/concrete Maintenance • Use ecosystem options (e.g., riparian mixtures Program Activities buffers) to naturally absorb excess water

• Track performance of flood control structures and assess whether additional redundant services or other options are required • Monitor changing environmental conditions affected by climate, including changes in storm surge levels, wind speed, and precipitation

FURTHER READING British Columbia Ministry of Environment, 2011. Climate Change Adaptation Guidelines for Sea Dikes and Coastal Flood Hazard Land Use. Available at http://www.env.gov.bc.ca/wsd/public_safety/flood/pdfs_word/draft_policy_rev.pdf U.S. Army Corps of Engineers, 2011. USACE Climate Change Adaptation Plan and Report 2011. Available at http://www.corpsclimate.us/docs/usace_ climate_change_adaptation_report_03_june_2011.pdf

Questions, feedback, suggestions, and requests for support should be sent to [email protected]. Published: November 2012

ADDRESSING CLIMATE CHANGE IMPACTS ON INFRASTRUCTURE: PREPARING FOR CHANGE FLOOD CONTROL STRUCTURES 3